Bottlenecks in traffic congestion are locations on a roadway where there is a temporary or permanent drop in capacity (defined as the maximum number of vehicle throughput per second) compared to immediately-adjacent downstream locations on the same roadway. Such circumstances can lead to traffic congestion and the formation of a queue of slow or stopped vehicles behind, or upstream of, the bottleneck. The detection and removal of bottlenecks is often a priority for organizations responsible for managing roadway networks, such as state departments of transportation or private entities operating toll roads. These organizations have an interest in knowing where a bottleneck is, how long the queue of vehicles behind it is, its duration (on a given day or period of interest) and how often it recurs (such as daily, occasionally, rarely).
A bottleneck head, often referred to as the bottleneck location or just bottleneck, is the point downstream of which roadway capacity increases and traffic again flows freely. The bottleneck head is therefore the point furthest along the roadway for which capacity is reduced. A bottleneck queue is the set of points on the roadway upstream of the bottleneck head in which traffic is moving slowly (or stopped) due to the reduced capacity at the bottleneck. The bottleneck head can therefore also be thought of as simply the most downstream point in the bottleneck queue.
A sustained bottleneck is one that persists for more than one time period of interest (such as 5 minutes). For example, a bottleneck may persist for several time periods adding up to a total of 45 minutes. A recurrent bottleneck is a bottleneck that is detected at an identical or similar place, and possibly time, over multiple days.
There are several established prior art methods of analyzing bottlenecks in traffic congestion. One well-known property of a bottleneck is a sudden increase in the speed of traffic as vehicles move downstream of (i.e., beyond) the front, or head, of the bottleneck. Existing techniques have used this property to detect bottlenecks from data generated from a linear sequence of detectors (such as inductive loop detectors placed every mile or so along a stretch of freeway). In one example, the bottleneck head may be defined as a point where the detected speed of downstream traffic is at least 20 mph faster than the detected speed of upstream traffic. The bottleneck queue is defined as all points immediately upstream of the bottleneck head for which the detected speed is less than 40 mph. This method, however, only applies to data on a linear sequence of points (such as inductive loop detector locations), typically corresponding to a single named roadway. There is no existing methodology for analyzing data to detect bottlenecks in a non-linear sequence of data points, and no existing methodology for analyzing complex bottlenecks comprised of more than one single named roadway.
The above-mentioned technique also attempts to examine recurring bottlenecks on the same or different days. For example, when for 5 out of 7 consecutive time periods, a bottleneck is detected with a head at location X, then the bottleneck is “sustained”. When a sustained bottleneck occurs on two different days, it is “recurrent”. This existing methodology checks for bottlenecks that are sustained or recurrent at exactly the same location during each time period or day. It does not, however, detect bottleneck head locations that vary across multiple time periods during the same day (e.g. 5 minute time periods), or across multiple days.